1. Field of the Invention
This invention relates generally to oxygen generating compositions, and more particularly concerns improved oxygen generation compositions containing a catalyst selected from copper oxide, nickel oxide, and a combination thereof.
2. Description of Related Art
Chemical oxygen generating compositions based upon the decomposition of alkali metal chlorates or perchlorates have long been used as an emergency source of breathable oxygen, such as in passenger aircraft, for example. Oxygen generating compositions utilizing alkali metal chlorates or perchlorates are disclosed in U.S. Pat. Nos. 5,198,147; 5,279,761; and 5,298,187; each of which are incorporated herein by reference.
A typical chemical oxygen generating candle may have several layers with different compositions and thus different reaction rates. Multiple layers are used in the candle instead of a single formula to help match the oxygen generation requirements, which vary with time as an airplane descends following a loss of cabin pressure. Different applications have different oxygen generation requirements. The candle typically has a generally cylindrical shape with a taper, with a recess at one end to hold an ignition pellet, which is typically ignited by firing a primer. The heat from the ignition pellet then ignites the reaction of the candle body and generates oxygen.
An aircraft oxygen generator is commonly preprogrammed according to the descent profile of a given type of airplane, and must meet the minimum oxygen flow requirement at all times during a descent. A conventional formulation of the oxygen generating composition generally can include an oxygen source such as a chlorate or perchlorate, a metal powder fuel such as iron powder, and cobalt oxide as a catalyst. Cobalt oxide has a very high catalytic activity in the decomposition of sodium chlorate, so that only a small amount of cobalt oxide (typically as low as 0.1%) is necessary to catalyze the decomposition of sodium chlorate. Such small amounts of the catalyst are difficult to uniformly distribute in a mixture of such an oxygen generating composition, so that an uneven distribution of cobalt oxide can result in variations in reactivity from core to core, and can result in low yields of satisfactory oxygen generating candles or cores. Oxygen generating compositions formulated with cobalt oxide and an inhibitor such as calcium hydroxide can have localized regions having a high cobalt oxide concentration and a low calcium hydroxide concentration occur due to imperfect mixing, with a far higher decomposition rate than other localized regions with a low cobalt oxide and a high calcium hydroxide concentration, leading to erratic and unpredictable performance.
Prolonged mixing is typically used to reduce irregularities in the distribution of the ingredients in cobalt oxide based oxygen generating compositions, increasing the difficulty in manufacturing and increasing manufacturing costs. However, loss of cobalt oxide in the mixer container such as on the mixer walls during preparation of core mixtures can also occur, resulting in performance variations from lot to lot. In addition, cobalt is a strategic metal, and is expensive.
Oxygen generating compositions utilizing manganese oxide as a catalyst for decomposition of chlorate or perchlorate to generate oxygen are known. However, use of manganese oxide as a catalyst produces a high concentration of chlorine in the oxygen gas released. A ferrate catalyzed formulation is also known, which also utilizes barium peroxide to modify the reaction. However, barium peroxide is toxic, and disposal of expended and scrap oxygen generators containing barium peroxide is expensive. It would be desirable to provide an improved oxygen generating formulation in which a uniformity of distribution of ingredients is easier to achieve, which will produce a greater uniformity of performance, and is easier to manufacture than conventional formulations. The present invention meets these needs.